Definition
A visual landing aid located beside the runway, consisting of a row of (usually four) light units that show a combination of red and white lights to indicate whether the aircraft is above, on, or below the correct glidepath to the runway threshold. The standard glidepath angle is normally 3 degrees, though it can be adjusted for specific runways.
Plain English
A row of lights next to the runway that tells the pilot, by colour, if they are flying the right slope down to land. White lights mean too high, red lights mean too low, and a mix of red and white means just right.
Context Anchor
Seen beside many runways during the landing approach, especially when a pilot needs a visual check against optical illusions.
Derivation
Precision' here means accurate or finely adjusted, not 'perfect.' 'Approach' refers to the final descent toward landing, and 'Path Indicator' simply means something that shows the correct track. Together: a precise visual guide showing the correct descent path to the runway.
Why Pilots Care
Prevents landing short or long of the intended touchdown point by giving immediate visual feedback on glide path position.
Grounding Statement
As you line up to land, the red and white lights give you a quick visual check of your descent path.
Intuition Check
Do not confuse “Precision Approach Path Indicator” with a full instrument landing procedure. It is a visual light aid for the landing path, not a system that flies the approach for you.
Example Sentence 1
On final approach at night, the pilot adjusted the descent rate slightly when the PAPI showed three white lights and one red.
Example Sentence 2
When runway lighting alone created an optical illusion at night, the Precision Approach Path Indicator helped the pilot maintain a safe descent angle.